Optical glass, press-molding glass gob and optical element

ABSTRACT

An optical glass whose refractive index is high and whose coloring is decreased comprising, by weight %, 2 to 45% of B 2 O 3 , 0 to 30% of SiO 2  provided that the content of B 2 O 3 &gt;the content of SiO 2 , 10 to 50% of La 2 O 3 , 0 to 30 % of TiO 2 , 0 to 15% of ZnO, 0 to 15% of ZrO 2 , 0 to 35% of Nb 2 O 5 , 0 to 35% of BaO, 0 to 5% of SrO, 0% or more but less than 8% of CaO, 0% or more but less than 13% of MgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% of Gd 2 O 3 , 0 to 15% of Y 2 O 3 , 0 to 18% of Ta 2 O 5 , 0% or more but less than 0.5% of WO 3 , 0 % or more but less than 1.5% of a total of Na 2 O, K 2 O and Li 2 O, 0 to 10% of GeO 2 , 0 to 20% of Bi 2 O 3 , 0 to 10% of Yb 2 O 3 , 0 to 10% of Al 2 O 3 , 0% or more but less than 2% of Sb 2 O 3  and 0 to 1% of SnO 2 .

FIELD OF THE INVENTION

[0001] The present invention relates to an optical glass, apress-molding glass gob (a glass gob for press-molding) and an opticalelement. More specifically, the present invention relates to an opticalglass whose refractive index is high and whose coloring is decreased, apress-molding glass gob formed of the optical glass and an opticalelement formed of the optical glass.

TECHNICAL BACKGROUND

[0002] In recent years, with the wide spread of digital cameras, smalllenses are increasingly demanded. A high-refractivity glass is suitableas an optical glass material for producing such small lenses. However,any conventional glass has a disadvantage that the coloring tendency ofthe glass is increasingly intensified with an increase in refractiveindex. Particularly, a digital camera uses CCD as an image-sensingdevice, and it therefore has a problem that the sensitivity to blue onthe short wavelength side out of three primary colors is attenuated whenan entire image-sensing unit is taken into account. JP-A-53-4023discloses a high-refractivity low-dispersion optical glass as a glassfor use in the above field. The problem with this glass is that it isrequired to use expensive HfO₂.

SUMMARY OF THE INVENTION

[0003] Under the circumstances, it is an object of the present inventionto provide an optical glass whose refractive index is high and whosecoloring is decreased, a press-molding glass gob formed of the aboveoptical glass and an optical element formed of the above optical glass.

[0004] For achieving the above object, the present inventor has madediligent studies and as a result has found that the above object can beachieved by an optical glass having a specific glass composition. Thepresent invention has been completed on the basis of the above finding.

[0005] That is, the subject matters of the present invention are asfollows.

[0006] (1) An optical glass comprising, by weight %, 2 to 45% of B₂O₃, 0to 30% of SiO₂ provided that the content of B₂O₃>the content of SiO₂, 10to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0to 35% of Nb₂O₅, 0 to 35% of BaO, 0 to 5% of SrO, 0% or more but lessthan 8% of CaO, 0% or more but less than 13% of MgO, provided that thetotal content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% of Gd₂O₃, 0to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than 0.5% of WO₃,0% or more but less than 1.5% of a total of Na₂O, K₂O and Li₂O, 0 to 10%of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0% ormore but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂.

[0007] (2) The optical glass of above (1), which has an refractive index(nd) of 1.8 to 2.1 and an Abbe's number (νd) of 20 to 40.

[0008] (3) The optical glass of above (1), which contains 2 to 45% ofB₂O₃, 0 to 30% of SiO₂, provided that the content of B₂O₃>the content ofSiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% ofZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0 to 5% of SrO, 0% or more butless than 8% of CaO, 0% or more but less than 13% of MgO, provided thatthe total content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% ofGd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than0.5% of WO₃, 0% or more but less than 1.5% of a total of Na₂O, K₂O andLi₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10%of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂, andhas a refractive index of more than 1.86 but up to 2.1, wherein theoptical glass exhibits λ₇₀ at 460 nm or less.

[0009] (4) The optical glass of above (1), which contains 2 to 45% ofB₂O₃, 0 to 30% of SiO₂, provided that the content of B₂O₃>the content ofSiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% ofZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0% or more but less than 2% ofSrO, 0% or more but less than 8% of CaO, 0% or more but less than 13% ofMgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or morebut less than 0.5% of WO₃, 0% or more but less than 1.5% of a total ofNa₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% ofYb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to1% of SnO₂, and has a refractive index of 1.8 to 1.86, wherein theoptical glass exhibits λ₇₀ at 460 nm or less.

[0010] (5) The optical glass of above (1), which contains 2 to 45% ofB₂O₃, 0 to 30% of SiO₂, provided that the content of B₂O₃>the content ofSiO₂), 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15%of ZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0% or more but less than 1%of SrO, 0% or more but less than 8% of CaO, 0% or more but less than 13%of MgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or morebut less than 0.5% of WO₃, 0% or more but less than 1.5% of a total ofNa₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% ofYb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to1% of SnO₂, and has a refractive index of 1.8 to 2.1, wherein theoptical glass exhibits λ₇₀ at 460 nm or less.

[0011] (6) The optical glass of above (1), which contains 2 to 45% ofB₂O₃, 0 to 30% of SiO₂, provided that the content of B₂O₃>the content ofSiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% ofZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0 to 0.8% of SrO, 0 to 7% ofCaO, 0 to 12% of MgO, provided that the total content of BaO, SrO, CaOand MgO is 0 to 40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% ofTa₂O₅, 0 to 0.4% of WO₃, 0 to 1.2% of a total of Na₂O, K₂O and Li₂O, 0to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃,0 to 1.8% of Sb₂O₃ and 0 to 1% of SnO₂, wherein the optical glassexhibits λ₇₀ at 460 nm or less.

[0012] (7) The optical glass of above (1), which contains 2 to 45% ofB₂O₃, 0 to 30% of SiO₂, provided that the content of B203>the content ofSiO₂), 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15%of ZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0% or more but less than 1%of SrO, 0% or more but less than 8% of CaO, 0% or more but less than 13%of MgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0% or more but less than 2% of Y₂O₃, 0 to 18% ofTa₂O₅, 0% or more but less than 0.5% of WO₃, 0% or more but less than1.5% of a total of Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% ofBi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2%of Sb₂O₃ and 0 to 1% of SnO₂.

[0013] (8) The optical glass of above (7), which contains 3 to 24% ofB₂O₃, 0 to 18% of SiO₂, provided that the weight ratio of the content ofB₂O₃/the content of SiO₂ is at least 1.1 or that no SiO₂ is contained,18 to 47% of La₂O₃, 0 to 26% of TiO₂, 0 to 12% of ZnO, 0 to 10% of ZrO₂,0 to 30% of Nb₂O₅, 0 to 32% of BaO, 0 to 10% of Gd₂O₃ and 0 to 4% ofYb₂O₃.

[0014] (9) The optical glass of above (7) or (8), which contains 1 to 5%of ZnO.

[0015] (10) The optical glass of above (1), wherein the total content ofB₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅, TiO₂, BaO, CaO, SrO, Gd₂O₃, Y₂O₃,Ta₂O₅, WO₃, Na₂O, K₂O, Li₂O, GeO₂, Yb₂O₃, Sb₂O₃ and SnO₂ is 99% or more.

[0016] (11) The optical glass of above (10), wherein the total contentof B₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅, TiO₂, BaO and Sb₂O₃ is 99% ormore.

[0017] (12) The optical glass of above (11), which contains all of B₂O₃,SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅, TiO₂ and BaO.

[0018] (13) The optical glass of above (1), which contains TiO₂.

[0019] (14) A press-molding glass gob which is formed of the opticalglass recited in above (1) and is to be softened under heat andpress-molded.

[0020] (15) An optical element formed of the optical glass recited inabove (1).

[0021] According to the present invention, there is provided an opticalglass whose refractive index is high and whose coloring is reduced.

[0022] According to the present invention, further, there is provided apress-molding glass gob for producing, by press-molding, an opticalelement formed of an optical glass whose refractive index is high andwhose coloring is decreased.

[0023] Further, according to the present invention, there is provided anoptical element formed of an optical glass whose refractive index ishigh and whose coloring is decreased.

PREFERRED EMBODIMENTS OF THE INVENTION

[0024] The optical glass of the present invention comprises, by weight%, 2 to 45% of B₂O₃, 0 to 30% of SiO₂ provided that the content ofB₂O₃>the content of SiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15%of ZnO, 0 to 15% of ZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0 to 5% ofSrO, 0% or more but less than 8% of CaO, 0% or more but less than 13% ofMgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or morebut less than 0.5% of WO₃, 0% or more but less than 1.5% of a total ofNa₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% ofYb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to1% of SnO₂.

[0025] According to the above optical glass, a high transmittance can beobtained in a visible light region, and particularly, a hightransmittance can be obtained in the short wavelength region of thevisible light region.

[0026] Further, there can be obtained an optical glass that is morestabilized in the ranges of a refractive index (nd) of 1.8 to 2.1 and anAbbe's number (νd) of 20 to 40.

[0027] The above compositional ranges will be explained in detail below.The following content by % in each component below represents weight %.

[0028] B₂O₃ is a component effective as an oxide for forming a glassnetwork of the above glass and is also effective for decreasing thetemperature for meltability and flow viscosity of the glass, and atleast 2% of B₂O₃ is required. However, the content of B₂O₃ exceeds 45%,the refractive index decreases. The content of B₂O₃ is therefore limitedto 2 to 45%, and it is preferably 3 to 24%, more preferably 5 to 18%.

[0029] SiO₂ works to maintain the devitrification resistance of theabove glass. When incorporated, SiO₂ works as a component for forming aglass network. However, when the content of SiO₂ exceeds 30%, themeltability of the glass is degraded, and it is difficult to produce theglass stably. The content of SiO₂ is therefore limited to 0 to 30%, andit is preferably 0 to 18%, more preferably 1 to 18%.

[0030] Further, when the content of B₂O₃ is smaller than the content ofSiO₂, the glass comes to be easily colored, and the glass is degraded inmeltability and devitrification resistance, so that more B₂O₃ isincorporated than SiO₂.

[0031] La₂O₃ is an essential component for obtaining a high-refractivitylow-dispersion glass. When the content of La₂O₃ is less than 10%, therefractive index decreases, and when it is larger than 50%, thedevitrification resistance decreases, so that it is difficult to obtaina glass that can be stably produced. The content of La₂O₃ is thereforelimited to 10 to 50%, and it is preferably 18 to 47%, more preferably 25to 47%.

[0032] TiO₂ is a component for improving the glass in chemicaldurability and devitrification resistance while adjusting opticalproperties such as a refractive index and an Abbe's number. Forimparting the glass with the above properties, it is required toincorporate 0 to 30% of TiO₂, and the content thereof is preferably 0 to26%, more preferably 1 to 26%, still more preferably 8 to 26%.

[0033] ZnO is a component for imparting the glass with high refractivityand low-dispersion properties (the degree of dependency of therefractive index on wavelengths is small), and it is also a componentfor improving the glass in devitrification resistance and decreasing thetemperature for viscous flowability. When the content of ZnO is largerthan 15%, the degree of devitrification increases, and it is difficultto obtain a glass that can be stably produced. The content of ZnO istherefore limited to 0 to 15%, and it is preferably 0 to 12%. When aproper amount of ZnO is added, the spectral transmittance on the shortwavelength end sharply rises. Therefore, the content of ZnO ispreferably more than 0%, but not more than 5%, more preferably 0.5 to5%, still more preferably 1 to 5%.

[0034] ZrO₂ is a component for producing a high refractive index, andwhen added in a small amount, it has an effect that the glass isimproved in devitrification resistance. However, when the contentthereof exceeds 15%, the devitrification resistance decreases, and themeltability of the glass is also degraded. The content of ZrO₂ istherefore limited to 0 to 15%, and it is preferably 0 to 10%, morepreferably 1 to 10%.

[0035] Nb₂O₅ is a component for imparting the glass with a highrefractive index, and it also has an effect that the glass is improvedin devitrification. The content of Nb₂O₅ is properly 0 to 35%. When thecontent of Nb₂O₅ exceeds 35%, the absorption on the short wavelengthside is intensified, and the coloring tendency is intensified. Thecontent of Nb₂O₅ is preferably 0 to 30%, more preferably 1 to 30%, stillmore preferably 1 to 20%, further more preferably 1 to 15%.

[0036] When used in the form of carbonate or nitrate as raw materials,BaO, SrO, CaO and MgO have an effect that the defoaming of the glass ispromoted.

[0037] When added in an amount of 0 to 35%, BaO has an effect that theglass is improved in coloring. When the content of BaO exceeds 35%,however, the devitrification resistance is degraded. The content of BaOis preferably 0 to 32%, more preferably 1 to 32%, still more preferably1 to 25%.

[0038] SrO may be added in an amount of 0 to 5% as a substitute for BaO.Similarly, 0% or more but less than 8% of CaO and 0% or more but lessthan 13% of MgO may be added. SrO can improve the glass indevitrification resistance when the glass is re-heated and molded, sothat the content of SrO is preferably 0% or more but less than 1%.Particularly, when the refractive index (nd) is 1.8 to 1.86, it isrequired to take care of a decrease in the above devitrificationresistance. When the refractive index (nd) is 1.8 to 1.86, preferably,the content of SrO is adjusted to 0% or more but less than 1%, and whenrefractive index (nd) is more than 1.86 to 2.1, preferably, the contentof SrO is adjusted to 0 to 5%. When the refractive index (nd) is 1.8 to2.1, more preferably, the content of SrO is adjusted to 0 to 0.8%.Further, when the total content of BaO, SrO, CaO and MgO exceeds 40%,the glass is degraded in devitrification resistance, and it is difficultto obtain a glass that can be stably produced. The total content of BaO,SrO, CaO and MgO is therefore limited to 0 to 40%.

[0039] Gd₂O₃ can be added in an amount up to 20% as a substitute forLa₂O₃. When the content of Gd₂O₃ exceeds 20%, the glass is degraded indevitrification resistance, and it is difficult to obtain a glass thatcan be stably produced. The content of Gd₂O₃ is therefore limited to 0to 20%, and it is preferably 0 to 10%.

[0040] Y₂O₃ and Yb₂O₃ can be also added in an amount of 0 to 15% and 0to 10%, respectively, as substitutes for La₂O₃. However, when thecontents of these components exceed the above upper limits, the glass isdegraded in devitrification resistance, and it is difficult to obtain aglass that can be stably produced. Preferably, the content of Y₂O₃ is 0%or more but less than 2%, and the content of Yb₂O₃ is 0 to 4%. Thecontent of Y₂O₃ is more preferably in the range of 0 to 1.5%.

[0041] Ta₂O₅ is a component for imparting the glass withhigh-refractivity and low-dispersion properties and is useful forforming a low-dispersion glass. However, when the content of Ta₂O₅exceeds 18%, the glass is degraded in meltability. The content of Ta₂O₅is therefore properly 0 to 18%.

[0042] WO₃ is a component for improving the glass in devitrificationresistance when added in a small amount. However, when the content ofWO₃ exceeds 0.5%, the absorption of light in a short wavelength regionby the glass is intensified, and the glass is strongly liable to becolored. The content of WO₃ is therefore limited to 0% or more but lessthan 0.5%, and it is preferably 0 to 0.4

[0043] Na₂O, K₂O and Li₂O are components effective for decreasing theglass transition temperature (Tg). Particularly, Li₂O has a remarkablyhigh effect on the above decrease. Since, however, these componentscause the glass to suffer a large decrease in devitrification resistanceand refractive index, the total content of Na₂O, K₂O and Li₂O istherefore limited to 0% or more but less than 1.5%.

[0044] GeO₂ has an effect similar to that of SiO₂, and it can be addedin an amount up to 10%. When the content of GeO₂ exceeds 10%, thedevitrification resistance decreases. The content of GeO₂ is thereforeproperly 0 to 10%. However, the above optical glass can attain desiredproperties without GeO₂. Preferably, GeO₂ that is expensive is thereforenot incorporated.

[0045] When added in a small amount, Bi₂O₃ has an effect that the glasstransition temperature (Tg) is decreased. When the content of Bi₂O₃exceeds 20%, the devitrification resistance decreases, and it causes theglass to be colored. The content of Bi₂O₃ is therefore properly 0 to 20

[0046] When added in a small amount, Al₂O₃ sometimes works to improvethe glass in devitrification resistance. However, the refractive indexdecreases at the same time. The content of Al₂O₃ is therefore limited to0 to 10%.

[0047] Ga₂O₃ and In₂O₃ can be also added in an amount up toapproximately 10%. However, when added, they may degrade thedevitrification resistance and they are expensive materials. Desirably,therefore, Ga₂O₃ and In₂O₃ are not incorporated.

[0048] In addition to the above components, Sb₂O₃ and SnO₂ that aregenerally used as a clarifying agent may be added. The content of Sb₂O₃is 0% or more but less than 2%, and the content of SnO₂ is 0 to 1%.

[0049] However, As₂O₃ that strongly works as a clarifying agent hastoxicity, so that it is desirable to add no As₂O₃.

[0050] In addition to the above oxides, desirably, lead, a lead compoundand radioactive substances such as U and Th are not incorporated.Further, from the viewpoint of decreasing the coloring of the glass, itis necessary to avoid the incorporation of substances that cause theglass to be colored, such as Cu, Cr, V, Fe, Ni and Co. Further, it isnecessary to avoid the addition of Te, Se and Cd.

[0051] In addition, the above JP-A-53-4023 describes an optical glasscontaining expensive HfO₂ as an essential component. In the presentinvention, however, the intended optical glass can be obtained withoutincorporating HfO₂.

[0052] Compositions having any combinations of preferred contents of theabove components in the above explanations are preferred for obtainingdesired optical glasses.

[0053] In the optical glass of the present invention, the refractiveindex (nd) and the Abbe's number (νd) are preferably in the range of 1.8to 2.1 (refractive index (nd)) and in the range of 20 to 40 (Abbe'snumber (νd)). The Abbe's number (vd) is more preferably in the range of20 to 39, and the refractive index (nd) is more preferably 1.81 to 2.1,still more preferably 1.85 to 2.1.

[0054] The transmittance property of the optical glass of the presentinvention will be explained below. The transmittance is quantitativelyevaluated as follows. First, a sheet glass having a thickness of 10mm±0.1 mm is prepared. The sheet glass is formed of the above opticalglass and has two surfaces that are lapped so as to be in parallel witheach other. Light is allowed to perpendicularly enter the lapped surfaceof the above sheet glass, and the sheet glass is measured for a spectraltransmittance including a surface reflection loss, in the wavelengthregion of 280 nm to 700 nm. A wavelength at which the spectraltransmittance comes to be 70% is taken as a wavelength λ₇₀, and awavelength at which the spectral transmittance comes to be 5% is takenas a wavelength 5. In the wavelength region from 280 nm to 700 nm,preferably, only one single wavelength λ₇₀ and only one singlewavelength λ₅ are present. And, desirably, the optical glass exhibits aspectral transmittance of at least 5% in the entire wavelength regionfrom λ₅ to 700 and a spectral transmittance of at least 70% in theentire wavelength region from λ₇₀ to 700 nm.

[0055] When λ₇₀ and λ₅ are adjusted to be present on a shorterwavelength side, an optical glass having the above transmittanceproperty comes to exhibit a higher transmittance in a broad range of thevisible light region.

[0056] In the present invention, the optical glass is preferably anoptical glass that exhibits λ₇₀ at 460 nm or at a shorter wavelength,more preferably an optical glass that exhibits λ₇₀ at 450 nm or at ashorter wavelength, still more preferably an optical glass that exhibitsλ₇₀ at 440 nm or at a shorter wavelength. For imparting the glass withvarious properties including the above refractive index and Abbe'snumber, more preferably, λ₇₀ is in the range of 350 to 460 nm, stillmore preferably, λ₇₀ is in the range of 350 to 450 rm, further morepreferably, λ₇₀ is in the range of 350 to 440 nm.

[0057] In the present invention, the optical glass is preferably anoptical glass that exhibits λ₅ at 400 nm or at a shorter wavelength,more preferably an optical glass that exhibits λ₅ at 390=m or at ashorter wavelength. For imparting the glass with various propertiesincluding the above refractive index and Abbe's number, more preferably,λ₅ is in the range of 300 to 390 nm.

[0058] Further, the optical glass of the present invention is furthermore preferably an optical glass that exhibits λ₇₀ and λ₅ which satisfythe above ranges at the same time.

[0059] Since λ₇₀ and λ₅ (particularly λ₇₀) are liable to change underglass melting conditions, it is necessary to take account of the meltingtemperature and the melting time period so that λ₇₀ and λ₅ can be on ashorter wavelength side. It is also necessary to reduce impurities thatcause coloring.

[0060] Examples of more preferred compositions, preferred opticalconstants and preferred ranges of λ₇₀ are as described below.

[0061] (Optical Glass 1)

[0062] An optical glass containing 2 to 45% of B₂O₃, 0 to 30% of SiO₂,provided that the content of B₂O₃>the content of SiO₂, 10 to 50% ofLa₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% ofNb₂O₅, 0 to 35% of BaO, 0 to 5% of SrO, 0% or more but less than 8% ofCaO, 0% or more but less than 13% of MgO, provided that the totalcontent of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% of Gd₂O₃, 0 to15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than 0.5% of WO₃, 0%or more but less than 1.5% of a total of Na₂O, K₂O and Li₂O, 0 to 10% ofGeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0% ormore but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂, and having arefractive index of more than 1.86 but up to 2.1, wherein the opticalglass exhibits 70 at 460 nm or less.

[0063] (Optical Glass 2)

[0064] An optical glass containing 2 to 45% of B₂O₃, 0 to 30% of SiO₂,provided that the content of B₂O₃>the content of SiO₂), 10 to 50% ofLa₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% ofNb₂O₅, 0 to 35% of BaO, 0% or more but less than 2% of SrO, 0% or morebut less than 8% of CaO, 0% or more but less than 13% of MgO, providedthat the total content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% ofGd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than0.5% of WO₃, 0% or more but less than 1.5% of a total of Na₂O, K₂O andLi₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10%of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂, andhaving a refractive index of 1.8 to 1.86, wherein the optical glassexhibits λ₇₀ at 460 nm or less.

[0065] (Optical Glass 3)

[0066] An optical glass containing 2 to 45% of B₂O₃, 0 to 30% of SiO₂,provided that the content of B₂O₃>the content of SiO₂), 10 to 50% ofLa₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% ofNb₂O₅, 0 to 35% of BaO, 0% or more but less than 1% of SrO, 0% or morebut less than 8% of CaO, 0% or more but less than 13% of MgO, providedthat the total content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% ofGd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than0.5% of WO₃, 0% or more but less than 1.5% of a total of Na₂O, K₂O andLi₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10%of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂, andhaving a refractive index of 1.8 to 2.1, wherein the optical glassexhibits λ₇₀ at 460 nm or less.

[0067] (Optical Glass 4)

[0068] An optical glass containing 2 to 45% of B₂O₃, 0 to 30% of SiO₂,provided that the content of B₂O₃> the content of SiO₂), 10 to 50% ofLa₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% ofNb₂O₅, 0 to 35% of BaO, 0 to 0.8% of SrO, 0 to 7% of CaO, 0 to 12% ofMgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0 to 0.4%of WO₃, 0 to 1.2% of a total of Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0 to 1.8% ofSb₂O₃ and 0 to 1% of SnO₂, wherein the optical glass exhibits λ₇₀ at 460nm or less.

[0069] (Optical Glass 5)

[0070] An optical glass containing 2 to 45% of B₂O₃, 0 to 30% of SiO₂,provided that the content of B₂O₃> the content of SiO₂), 10 to 50% ofLa₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% ofNb₂O₅, 0 to 35% of BaO, 0% or more but less than 1% of SrO, 0% or morebut less than 8% of CaO, 0% or more but less than 13% of MgO, providedthat the total content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% ofGd₂O₃, 0% or more but less than 2% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% ormore but less than 0.5% of WO₃, 0% or more but less than 1.5% of a totalof Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% ofYb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to1% of SnO₂.

[0071] (Optical Glass 6)

[0072] An optical glass that is included in the above optical glass 5and which contains 3 to 24% of B₂O₃, 0 to 18% of SiO₂, provided that theweight ratio of the content of B₂O₃/the content of SiO₂ is at least 1.1or that no SiO₂ is contained, 18 to 47% of La₂O₃, 0 to 26% of TiO₂, 0 to12% of ZnO, 0 to 10% of ZrO₂, 0 to 30% of Nb₂O₅, 0 to 32% of BaO, 0 to10% of Gd₂O₃ and 0 to 4% of Yb₂O₃.

[0073] (Optical Glass 7)

[0074] An optical glass that is included in the above optical glass 5 or6 and which contains 1 to 5% of ZnO.

[0075] (Optical Glass 8)

[0076] An optical glass that is included in any one of the above opticalglasses 1 to 7 and wherein the total content of B₂O₃, SiO₂, La₂O₃, ZnO,ZrO₂, Nb₂O₅, TiO₂, BaO, CaO, SrO, Gd₂O₃, Y₂O₃, Ta₂O₅, WO₃, Na₂O, K₂O,Li₂O, GeO₂, Yb₂O₃, Sb₂O₃ and SnO₂ is 99% or more, more preferably 100%.

[0077] (Optical Glass 9)

[0078] An optical glass that is included in the above optical glass 8and where the total content of B₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅,TiO₂, BaO and Sb₂O₃ is 99% or more, more preferably 100%.

[0079] (Optical Glass 10)

[0080] An optical glass that is included in the above optical glass 9and which contains all of B₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅, TiO₂ andBaO.

[0081] (Optical Glass 11)

[0082] An optical glass that is included in any one of the above opticalglasses 1 to 11 and which contains TiO₂. In this optical glass, theweight ratio of the content of Nb₂O₅/the content of TiO₂ is preferablyfrom 0 to 7, more preferably from 0 to 6. In this constitution, anoptical glass to be colored to less degree can be obtained.

[0083] Having the above transmittance property, the optical glass of thepresent invention exhibits a high transmittance to light in a shortwavelength region of the visible light region, so that a well-balancedimage-sensing optical system can be easily constituted. The opticalglass of the present invention is particularly suitable as a materialfor an optical element such as a lens for constituting an image-sensingsystem for a solid image-sensing device.

[0084] The liquidus temperature of the optical glass of the presentinvention will be explained below. In the optical glass of the presentinvention, the liquidus temperature is preferably 1,250° C. or lower,more preferably 1,200° C. or lower. As far as the stability of the glassis concerned, an optical glass that shows no liquidus temperature ispreferred. For imparting the glass with the above various properties,however, the optical glass of the present invention has a liquidustemperature of 900 to 1,200° C.

[0085] The press-molding glass gob of the present invention and themethod for preparation thereof will be explained below. Thepress-molding glass gob is a glass molded material that is to besoftened under heat and press-molded, and it is also called apress-molding preform (preform for press-molding). The weight and formof the press-molding glass gob are determined as required depending upona press-molded product as an end product. The press-molding glass gob ofthe present invention is formed of the above optical glass and hasvarious properties that reflect the various properties of the opticalglass of the present invention.

[0086] In the method for preparing the above press-molding glass gob, amolten glass is shaped into a moldable glass gob formed of the aboveoptical glass. First, glass raw materials for obtaining the opticalglass of the present invention are formulated, dissolved, clarified andhomogenized to obtain a homogeneous molten glass free of gas bubbles andforeign matter. Then, the molten glass is flowed out from a flow pipemade of a platinum alloy, or the like. For flowing the molten glass out,the temperature of the flow pipe, etc., are arranged such that the glassis not devitrified. The molten glass that flows out is cast into areceiving mold or a casting mold to shape the molten glass into apredetermined form. Methods suitable for the above shaping will bedescribed as examples.

[0087] The first shaping method is a method in which a plurality ofreceiving molds are consecutively transferred into a place below theflow pipe to receive a molten glass gob having a predetermined weight oneach receiving mold and each glass gob is cooled while each is shaped.In this method, a forward end of the molten glass flow flowing out ofthe pipe is supported on a receiving mold, and the receiving mold israpidly moved down timely when a molten glass gob having a predeterminedweight can be separated. In this case, the supply of the molten glassonto the receiving mold does not keep up with the downward movement ofthe receiving mold, and a leading molten glass flow is separated from amolten glass on the backward side of the flow, so that a predeterminedweight of the molten glass gob can be received on the receiving mold. Inthis manner, a glass can be shaped without leaving a cut mark (shearmark) formed when a molten glass flow is cut with a blade. In the abovefirst method, a glass gob having a weight equivalent to, or a littlelarger than, a press-molding glass gob can be shaped.

[0088] When a glass gob having a weight equivalent to the weight of onepress-molding glass gob is shaped, this glass gob can be used as apress-molding glass gob. In this case, it is preferred to cool the glassgob at such a rate that the glass is not broken.

[0089] When a glass gob having a weight larger than the weight of onepress-molding glass gob is shaped, this glass gob is annealed to reducestrains and then machined to complete a glass gob having a weightequivalent to the weight of one press-molding glass gob, and thecompleted glass gob is used as a press-molding glass gob. According tothis method, glass gobs are prepared beforehand, and the glass gobs aremachined depending upon demands to adjust their weights, whereby therecan be supplied press-molding glass gobs that can be press-molded intooptical elements having various sizes. For the above machining, barrellapping is preferred.

[0090] Further, when the above press-molding glass gob is used forprecision press-molding, a press-molding glass gob that is shapedwithout any machining is preferred.

[0091] The second shaping method is a method in which a molten glass iscast into a casting mold at a constant speed, the casting mold having anearly horizontal bottom surface and a pair of sidewalls facing eachother in parallel across the bottom surface. A cast molten glassuniformly spreads within the casting mold to be shaped into a glasssheet having a width determined by the distance of the above pair ofsidewalls. The thus-formed glass sheet is drawn out from an openingportion of the casting mold at a speed depending upon a molten glasssupply speed such that a sheet having a uniform thickness and a uniformwidth can be obtained. The thus-obtained glass sheet is annealed toreduce strains and then cut to a predetermined size. The thus-obtainedglass piece is called “cut piece”. The cut piece is chamfered asrequired or machined so as to have a weight equivalent to the weight toa press-molding glass gob. For chamfering the cut piece or machining thecut piece for adjusting its weight, barrel lapping is preferred.

[0092] In any one of the above methods, there can be obtained thepress-molding glass gob of the present invention, which has apredetermined weight and is formed of the optical glass of the presentinvention. In addition, a mold release film may be formed on thepress-molding glass gob, or a powdered mold release agent may be appliedthereto, as required for making it easy to separate a molded productfrom a mold when the press-molding is carried out. However, the powderedmold release agent is undesirable for precision press-molding, since themold release agent is transferred to the glass forming the glass gob(press-molded product).

[0093] The optical element of the present invention will be explainedbelow. The optical element of the present invention is formed of theabove optical glass of the present invention. The optical elementtherefore has various properties of the above optical glass. As atypical embodiment, the optical element of the present invention has arefractive index (nd) of 1.8 to 2.1 and an Abbe's number (νd) of 20 to40, and also commonly has the property of a high transmittance on ashort wavelength side of the visible light region. The optical elementformed of the above optical glass preferably exhibits λ₇₀ and λ₅ in theabove-described ranges, exhibits a high transmittance to visible lightand is free from coloring. This optical element is suitable for opticalsystems of cameras using a solid image-sensing device such as a digitalcamera, a video camera and a camera incorporated into a mobile item.

[0094] The optical element of the present invention includes variouslenses such as a spherical lens, an aspherical lens, a microlens and alens array, a prism and a diffraction grating. The optical element ofthe present invention may be provided with an optical thin film such asan anti-reflection film, a partial reflection film, a high reflectionfilm or the like as required.

[0095] The method for producing the optical element of the presentinvention will be explained below. In the method for producing theoptical element of the present invention, the above press-molding glassgob or a press-molding glass gob prepared by the above preparationmethod is softened under heat and press-molded with a press mold, toproduce the optical element.

[0096] The optical element has an optical-function surface having anoptical function, which refracts, transmits, diffract or reflects light.The press-molding method can be largely classified into the followingtwo methods depending upon how the above optical-function surface isformed.

[0097] The first method is a method in which a press-molded producthaving a form similar to an end optical element and having a larger sizethan the optical element is formed by press-molding. The press-moldedproduct is polished and/or lapped, and the surface of the opticalelement including the optical-function surface is formed by machining.Since the machining is carried out after the press-molding, it ispreferred to anneal the press-molded product to decrease strains inorder to prevent the breaking of the glass during the machining. In thismethod, the press-molding can be carried out in atmosphere, so that theabove powdered mold release agent may be used.

[0098] The second method is a so-called precision press-molding method,in which the molding surface of a press mold is precisely worked so asto have an inversion form of the form of an end optical element, a moldrelease film is optionally formed, and the form of the above moldingsurface is precisely transferred, by press molding, to a glass gob thatis softened under heat. According to this method, the optical-functionsurface can be formed by the press-molding without polishing or lapping.However, it is required to carry out the press-molding in anon-oxidizing atmosphere such as a nitrogen gas atmosphere.

[0099] In the above second method, it is not essential to machine thepress-molded product, so that a strain may remain so long as the strainhas no optical influence, and the annealing of the press-molded productcan be omitted. As a method for producing an optical element, further,there is another method in which a glass in a molten state is fed into apress mold to produce a press-molded product having a form similar tothe form of an optical element, and the press-molded product is polishedand lapped to complete an optical element.

[0100] The refractive index (nd) and the Abbe's number (νd) of theoptical element slightly change due to a thermal history during theprocess of producing the optical element. For producing an opticalelement having precisely determined optical constants, the glasscomposition and the thermal history during the production process can beadjusted by taking account of the above change in refractive index (nd)and Abbe's number (vd). In this manner, there can be provided an opticalelement that has predetermined optical constants and an excellenttransmittance and which is particularly suitable as an optical part fora machine, equipment or an item on which a solid image-sensing device,or the like is mounted.

EXAMPLES

[0101] The present invention will be explained further in detail withreference to Examples hereinafter, while the present invention shall notbe limited by these Examples.

Examples 1-11

[0102] A raw material batch formulated to give 100 g of a glass having acomposition shown in Table 1 or 2 was placed in a crucible formed ofplatinum and melted in a furnace set at 1,300° C., and a molten glass isstirred, clarified, then cast into a casting mold made of iron,maintained at a temperature around a glass transition temperature (Tg)for 2 hours and gradually cooled, to give an optical glass.

[0103] The thus-obtained optical glass in each Example was measured fora refractive index (nd), an Abbe's number (νd), a liquidus temperature(LT) and λ₇₀ and λ₅ as follows. Tables 1 and 2 show the results.

[0104] (1) Refractive Index (nd) and Abbe's Number (νd)

[0105] An optical glass obtained by cooling at a temperature-decreaserate of −30° C./h was measured.

[0106] (2) Liquidus Temperature (LT)

[0107] A plurality of crucibles made of platinum were prepared, and 50cm³ of glass was placed in each crucible. The crucibles with the glassin them were placed in furnaces in which the temperature was set atintervals of 10° C. and held under different temperature conditions for2 hours. After cooled, an inside of each glass was observed through amicroscope having a magnification of 100 times for the presence orabsence of a crystal, on the basis of which the liquidus temperature wasdetermined.

[0108] (3) λ₇₀ and λ₅

[0109] A 10 mm thick lapped sample was measured for spectraltransmittances, and a wavelength (nm) at which the sample exhibited atransmittance of 5% was determined as λ₅ and a wavelength (nm) at whichthe sample exhibited a transmittance of 70% was determined as λ₇₀. TABLE1 Examples 1 2 3 4 5 6 Glass composition B₂O₃ 13.16 8.20 13.16 13.0410.50 13.00 (wt %) SiO₂ 6.63 6.00 6.63 6.57 6.50 10.00 La₂O₃ 19.03 49.0036.19 35.85 34.00 37.00 ZnO 7.21 0.00 7.21 2.68 3.00 3.00 ZrO₂ 5.68 5.407.05 4.28 7.00 7.00 Nb₂O₅ 21.59 0.00 3.85 6.76 7.00 4.00 TiO₂ 3.94 4.409.04 12.44 16.00 9.00 BaO 21.94 0.00 16.86 18.38 16.00 17.00 CaO 0.000.00 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.00 0.00 0.00 0.00 (RO) (21.94)(0.00) (16.86) (18.38) (16.00) (17.00) Gd₂O₃ 0.00 0.00 0.00 0.00 0.000.00 Y₂O₃ 0.00 1.00 0.00 0.00 0.00 0.00 Ta₂O₅ 0.00 18.00 0.00 0.00 0.000.00 WO₃ 0.30 0.00 0.00 0.00 0.00 0.00 Na₂O 0.00 0.00 0.00 0.00 0.000.00 K₂O 0.52 0.00 0.00 0.00 0.00 0.00 Li₂O 0.00 0.00 0.00 0.00 0.000.00 (R₂O) (0.52) (0.00) (0.00) (0.00) (0.00) (0.00) GeO₂ 0.00 5.00 0.000.00 0.00 0.00 Bi₂O₃ 0.00 0.00 0.00 0.00 0.00 0.00 Yb₂O₃ 0.00 3.00 0.000.00 0.00 0.00 Total 100.00 100.00 100.00 100.00 100.00 100.00 P.Properties nd 1.8741 1.9225 1.87247 1.89803 1.94875 1.85403 νd 31.2735.95 34.21 31.14 28.25 34.95 λ₇₀ (nm) 397 405 402 407 418 391 λ₅ (nm)353 364 352 360 364 353 LT (° C.) 1160 1050 1080 1100 1150 1090

[0110] TABLE 2 Examples 7 8 9 10 11 Glass composition B₂O₃ 8.00 12.7023.00 13.2 8.0 (wt %) SiO₂ 6.00 6.30 0.00 6.6 6.0 La₂O₃ 34.00 33.6040.00 36.2 34.0 ZnO 2.50 2.50 5.00 2.7 2.0 ZrO₂ 6.50 6.50 5.00 5.7 6.5Nb₂O₅ 8.50 2.00 17.00 5.4 8.0 TiO₂ 19.00 5.00 5.00 13.4 20.5 BaO 15.5031.40 0.00 16.8 15.0 CaO 0.00 0.00 0.00 0.0 0.0 SrO 0.00 0.00 0.00 0.00.0 (RO) (15.50) (31.40) (0.00) (16.8) (15.0) Gd₂O₃ 0.00 0.00 0.00 0.00.0 Y₂O₃ 0.00 0.00 0.00 0.0 0.0 Ta₂O₅ 0.00 0.00 5.00 0.0 0.0 WO₃ 0.000.00 0.00 0.0 0.0 Na₂O 0.00 0.00 0.00 0.0 0.0 K₂O 0.00 0.00 0.00 0.0 0.0Li₂O 0.00 0.00 0.00 0.0 0.0 (R₂O) (0.00) (0.00) (0.00) (0.0) (0.0) GeO₂0.00 0.00 0.00 0.0 0.0 Bi₂O₃ 0.00 0.00 0.00 0.0 0.0 Yb₂O₃ 0.00 0.00 0.000.0 0.0 Total 100.00 100.00 100.00 100.0 100.0 P. Properties nd 1.99451.82546 1.90564 1.90047 2.00030 νd 25.88 38.6 31.71 30.71 25.51 λ₇₀ (nm)437 407 424 408 440 λ₅ (nm) 370 341 362 362 372 LT (° C.) 1150 1090 10501080 1150

[0111] Tables 1 and 2 show that the optical glasses of the presentinvention shown in Examples had a refractive index (nd) in the range of1.8 to 2.1 and an Abbe's number (νd) in the range of 20 to 40.

Example 12

[0112] Each of the clarified and homogenized molten glasses obtainedfrom the glasses in Examples 1 to 11 was independently cast from a pipeformed of platinum into a casting mold having one sidewall opened, at aconstant flow rate, and while a glass sheet having a constant thicknessand a constant width was formed, the glass sheet was drawn out of theopening portion of the casting mold. The glass sheet that was drawn outwas annealed in an annealing furnace to decrease strains. In thismanner, there were obtained glass sheets of the optical glasses of theabove Examples 1 to 11, which had strains decreased and were homogenous,colorless and free of foreign matter.

[0113] Each glass sheet was cut into small cubes to obtain a pluralityof cut pieces having identical dimensions. Further, a plurality of thecut pieces were barrel lapped so as to have an intended weight, and usedas press-molding glass gobs.

[0114] Besides the above method, there may be employed a method in whichthe above molten glass is flowed out from a nozzle formed of platinum ata constant speed, many receiving molds are transferred into a placebelow the nozzle one after another, to receive a molten glass gob oneach receiving mold, each molten glass gob is shaped into a sphericalform or a sphere-flattened form, annealed, then barrel-lapped to adjustthe weight of each to an intended weight, and the thus formed glass gobsare used as press-molding glass gobs.

Example 13

[0115] A powdered mold release agent was applied to the entire surfaceof each glass gob obtained in Example 12, and each glass gob wasindependently softened under heat with a heater and then charged into apress mold having an upper mold member and a lower mold member. Theglass gobs were respectively pressed with the press mold to give lensblanks having the form of a lens each.

[0116] Then, the lens blanks were annealed to remove strains and adjusttheir refractive indexes and Abbe's numbers to predetermined values. Thecooled lens blanks were polished and lapped to produce lenses. The abovesteps in series were carried out in atmosphere.

[0117] The thus-obtained lenses were excellent in transmittanceproperties and had various properties of the optical glasses of Examples1 to 11. An anti-reflection film may be formed on each lens as required.

[0118] The above lenses can constitute an excellent image-sensingoptical system.

[0119] Industrial Utility

[0120] The optical glass of the present invention has a high refractiveindex and has its coloring decreased, so that it can be suitably used inan image-sensing unit such as a digital camera using CCD as animage-sensing device.

1. An optical glass comprising, by weight %, 2 to 45% of B₂O₃, 0 to 30%of SiO₂ provided that the content of B₂O₃>the content of SiO₂, 10 to 50%of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35%of Nb₂O₅, 0 to 35% of BaO, 0 to 5% of SrO, 0% or more but less than 8%of CaO, 0% or more but less than 13% of MgO, provided that the totalcontent of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% of Gd₂O₃, 0 to15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than 0.5% of WO₃, 0%or more but less than 1.5% of a total of Na₂O, K₂O and Li₂O, 0 to 10% ofGeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0% ormore but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂.
 2. The optical glassof claim 1, which has an refractive index (nd) of 1.8 to 2.1 and anAbbe's number (νd) of 20 to
 40. 3. The optical glass of claim 1, whichcontains 2 to 45% of B₂O₃, 0 to 30% of SiO₂, provided that the contentof B₂O₃>the content of SiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0 to5% of SrO, 0% or more but less than 8% of CaO, 0% or more but less than13% of MgO, provided that the total content of BaO, SrO, CaO and MgO is0 to 40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅₁ 0% ormore but less than 0.5% of WO₃, 0% or more but less than 1.5% of a totalof Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% ofYb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to1% of SnO₂, and has a refractive index of more than 1.86 but up to 2.1,wherein the optical glass exhibits λ₇₀ at 460 nm or less.
 4. The opticalglass of claim 1, which contains 2 to 45% of B₂O₃, 0 to 30% of SiO₂,provided that the content of B₂O₃> the content of SiO₂, 10 to 50% ofLa₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% ofNb₂O₅, 0 to 35% of BaO, 0% or more but less than 2% of SrO, 0% or morebut less than 8% of CaO, 0% or more but less than 13% of MgO, providedthat the total content of BaO, SrO, CaO and MgO is 0 to 40%, 0 to 20% ofGd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0% or more but less than0.5% of WO₃, 0% or more but less than 1.5% of a total of Na₂O, K₂O andLi₂O, 0 to 10% of GeO₂, 0 to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10%of Al₂O₃, 0% or more but less than 2% of Sb₂O₃ and 0 to 1% of SnO₂, andhas a refractive index of 1.8 to 1.86, wherein the optical glassexhibits λ₇₀ at 460 nm or less.
 5. The optical glass of claim 1, whichcontains 2 to 45% of B₂O₃, 0 to 30% of SiO₂, provided that the contentof B₂O₃>the content of SiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to15% of ZnO, 0 to 15% of ZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0% ormore but less than 1% of SrO, 0% or more but less than 8% of CaO, 0% ormore but less than 13% of MgO, provided that the total content of BaO,SrO, CaO and MgO is 0 to 40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to18% of Ta₂O₅, 0% or more but less than 0.5% of WO₃, 0% or more but lessthan 1.5% of a total of Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20%of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than2% of Sb₂O₃ and 0 to 1% of SnO₂, and has a refractive index of 1.8 to2.1, wherein the optical glass exhibits λ₇₀ at 460 nm or less.
 6. Theoptical glass of claim 1, which contains 2 to 45% of B₂O₃, 0 to 30% ofSiO₂, provided that the content of B₂O₃> the content of SiO₂, 10 to 50%of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% of ZrO₂, O to 35%of Nb₂O₅, 0 to 35% of BaO, 0 to 0.8% of SrO, 0 to 7% of CaO, 0 to 12% ofMgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0 to 15% of Y₂O₃, 0 to 18% of Ta₂O₅, 0 to 0.4%of WO₃, 0 to 1.2% of a total of Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0to 20% of Bi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0 to 1.8% ofSb₂O₃ and 0 to 1% of SnO₂, wherein the optical glass exhibits λ₇₀ at 460nm or less.
 7. The optical glass of claim 1, which contains 2 to 45% ofB₂O₃, 0 to 30% of SiO₂, provided that the content of B₂O₃>the content ofSiO₂, 10 to 50% of La₂O₃, 0 to 30% of TiO₂, 0 to 15% of ZnO, 0 to 15% ofZrO₂, 0 to 35% of Nb₂O₅, 0 to 35% of BaO, 0% or more but less than 1% ofSrO, 0% or more but less than 8% of CaO, 0% or more but less than 13% ofMgO, provided that the total content of BaO, SrO, CaO and MgO is 0 to40%, 0 to 20% of Gd₂O₃, 0% or more but less than 2% of Y₂O₃, 0 to 18% ofTa₂O₅, 0% or more but less than 0.5% of WO₃, 0% or more but less than1.5% of a total of Na₂O, K₂O and Li₂O, 0 to 10% of GeO₂, 0 to 20% ofBi₂O₃, 0 to 10% of Yb₂O₃, 0 to 10% of Al₂O₃, 0% or more but less than 2%of Sb₂O₃ and 0 to 1% of SnO₂.
 8. The optical glass of claim 7, whichcontains 3 to 24% of B₂O₃, 0 to 18% of SiO₂, provided that the weightratio of the content of B₂O₃/the content of SiO₂ is at least 1.1 or thatno SiO₂ is contained, 18 to 47% of La₂O₃, 0 to 26% of TiO₂, 0 to 12% ofZnO, 0 to 10% of ZrO₂, 0 to 30% of Nb₂O₅, 0 to 32% of BaO, 0 to 10% ofGd₂O₃ and 0 to 4% of Yb₂O₃.
 9. The optical glass of claim 7 or 8, whichcontains 1 to 5% of ZnO.
 10. The optical glass of claim 1, wherein thetotal content of B₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂₀₅, TiO₂, BaO, CaO,SrO, Gd₂O₃, Y₂O₃, Ta₂O₅, WO₃, Na₂O, K₂O, Li₂O, GeO₂, Yb₂O₃, Sb₂O₃ andSnO₂ is 99% or more.
 11. The optical glass of claim 10, wherein thetotal content of B₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅, TiO₂, BaO andSb₂O₃ is 99% or more.
 12. The optical glass of claim 11, which containsall of B₂O₃, SiO₂, La₂O₃, ZnO, ZrO₂, Nb₂O₅, TiO₂ and BaO.
 13. Theoptical glass of claim 1, which contains TiO₂.
 14. A press-molding glassgob which is formed of the optical glass recited in claim 1 and is to besoftened under heat and press-molded.
 15. An optical element formed ofthe optical glass recited in claim 1.